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Polycyclic
aromatic hydrocarbons (PAHs) are compounds containing
two or more aromatic rings, fused together in
different arrangements to form numerous PAH isomers
and derivatives. PAHs can be formed by thermal
decomposition of any organic material containing
carbon and hydrogen. There are two main mechanisms
in the formation of PAHs: (1) pyrolysis and incomplete
combustion, and (2) carbonization process. Four
PAH compounds have been measured in this study.
A total 18 samples were collected. The measured
concentrations of PAHs found in this study are
plotted in Figure 4.1j.
The summary of statistical data is shown in Table
4.1c. Among the four PAHs, the concentrations
of anthracene were much higher than that of the
other three pollutants. The mean concentration
of anthracene was 3.70 ngm-3 and ranged from 1.45
to 7.33 ngm-3 (Figure
4.1k).
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Table
4.1c Summary of PAHs data at PolyU station
(n=18)
|
| Unit
(ngm-3) |
Max. |
Min. |
Average
|
Standard
deviation |
| Anthracene |
7.33 |
1.45 |
3.7 |
1.69 |
| Benzo(a)anthracene |
2.15 |
0.08 |
0.68 |
0.63 |
|
Benzo(a)pyrene
|
1.08 |
0.11 |
0.5 |
0.27 |
|
Chryrene
|
2.58 |
0.33 |
1.33 |
0.60 |
Monthly
variation of PAHs
The
monthly variations of PAHs are shown in Figure
4.1l. The line patterns for the selected PAHs
was similar but not exactly the same. This indicates
that there might be some interference from other
nearby emission sources.
Seasonal
Variation of PAHs at PolyU Station
The
seasonal variations of PAHs are shown in Figure
4.1m. The concentrations of all selected PAHs
were higher in winter than in summer. This is
because most PAHs are attached to particulates
and the rainier summer days cause them to be washed
out of the atmosphere.
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